1. Field of the Invention
The invention relates to a fuel reforming apparatus that produces a hydrogen-rich fuel gas from a raw fuel containing a hydrocarbon-containing compound, and to a technique for controlling the operation of the fuel reforming apparatus so as to remove carbon deposited in a reformer of the fuel reforming apparatus.
2. Description of Related Art
A known fuel reforming apparatus utilizes a steam-reforming reaction so as to generate a hydrogen-rich fuel gas from a raw fuel containing a hydrocarbon-containing compound(s). Since the steam reforming reaction is an endothermic reaction, the fuel reforming apparatus also utilizes a partial-oxidation reaction of the raw fuel, which is an exothermic reaction, as well as the steam reforming reaction. Thus, heat required for the steam reforming reaction is well balanced with heat generated through the exothermic partial-oxidation reaction. In operation, the amounts of the raw fuel, water and oxygen (air) to be supplied to the fuel reforming apparatus are optimally controlled in view of the balance between the steam reforming reaction and the partial-oxidation reaction. A known example of this type of fuel reforming apparatus is disclosed in Japanese Patent Laid-Open Publication No. 11-79703.
However, the known fuel reforming apparatus suffers from a problem that carbon produced through decomposition of the raw fuel is deposited and accumulated on a reforming catalyst, resulting in deterioration of the activity of the reforming catalyst. In particular, this problem of carbon deposition is significant or serious in the case where a raw fuel containing a higher hydrocarbon compound, such as gasoline, as a major component is used. Therefore, a technique for reducing an amount of carbon deposited and accumulated on the reforming catalyst has been desired.
It is an object of the invention to provide a fuel reforming apparatus capable of reducing an amount of carbon deposited and accumulated on a reforming catalyst thereof. It is another object of the invention to provide a method of controlling the fuel reforming apparatus so that the amount of carbon deposited and accumulated on the reforming catalyst can be reduced.
To accomplish the above and/or other object(s), there is provided according to one aspect of the invention a fuel reforming apparatus for reforming a raw fuel containing a hydrocarbon-containing compound so as to produce a hydrogen-rich fuel gas for use in a fuel cell. The fuel reforming apparatus includes (a) a reformer including a reforming catalyst, the reformer reforming the raw fuel by utilizing at least a steam reforming reaction and a partial oxidation reaction, (b) a raw fuel supply device that supplies the reformer with the raw fuel, (c) a water supply device that supplies the reformer with water so that at least a part of the supplied water is used for the steam reforming reaction, (d) an oxygen supply device that supplies the reformer with oxygen so that at least a part of the supplied oxygen is used for the partial oxidation reaction of the raw fuel at the reforming catalyst, and (e) a controller that controls the raw fuel supply device, the water supply device and the oxygen supply device. In the fuel reforming apparatus, the controller executes a carbon removal process for removing carbon deposited on the reforming catalyst under a predetermined condition, by controlling at least one of an amount of the raw fuel supplied to the reformer and an amount of the oxygen supplied to the reformer so that an O/C ratio of the number of oxygen atoms O supplied from the oxygen supply device to the number of carbon atoms contained in the raw fuel supplied from the raw fuel supply device becomes larger than an appropriate range of the O/C ratio that is to be established during a normal operation of the reformer.
In the fuel reforming apparatus as described above, the carbon removal process is executed so that the O/C ratio of the number of oxygen atoms O supplied to the reformer to the number of carbon atoms supplied to the reformer becomes larger than an appropriate range of the O/C ratio that is to be established during the normal operation of the reformer. Thus, the carbon accumulated on the reforming catalyst can be burned, resulting in a reduction in the amount of carbon deposited and accumulated on the reforming catalyst.
In one preferred embodiment of the invention, the controller intermittently executes the carbon removal process a plurality of times.
If the carbon removal process is continuously performed for a long time, the temperature of the reforming catalyst may be gradually increased. If the carbon removal process is finished, on the other hand, the temperature of the reforming catalyst is rapidly lowered. Accordingly, if the carbon removal process is intermittently executed a plurality of times, the amount of carbon accumulated on the reforming catalyst can be reduced while preventing undesirable heating of the reforming catalyst.
In the meantime, the present invention can be realized in various forms. For example, the invention may be realized or embodied in the form of a fuel reforming apparatus, a method of controlling the fuel reforming apparatus, a fuel cell system, a method of controlling the fuel cell system, a moving object having such a fuel reforming apparatus or fuel cell system, a method of controlling the moving object, a computer program that realizes any of these methods or functions of the apparatus or system, a recording medium that stores such a computer program, and a code or data signal which represents such a computer program and takes the form of a transmission wave.